The present invention relates to a clamping device for clamping a protective hood on the clamping collar of a hand-operated machine tool, especially of an angle grinder or such like electrical tool, according to the precharacterising clause of the main claim.
A clamping device of this type, in which each clamping-strap end has an outwardly bent tab, is known (German Offenlegungsschrift 3,638,337). The clamping lever engages with one end on a transmission member in the form of a clamping screw. For this purpose, the clamping lever is made approximately fork-shaped at its free end, the two fork legs engaging round the end of the clamping screw on both sides. A bolt passes through the clamping screw and the two fork legs and allows a pivotability of the clamping lever about the thus predetermined pivot axis in respect of the transmission member and of the first clamping-strap end adjacent to the latter. The clamping screw engages at an axial distance from the first clamping-strap end on the bent tab of the other clamping-strap end, in that an adjustable nut is screwed onto this end and is supported axially on the tab of the second clamping-strap end. The clamping lever is equipped, between the pivot axis and the bent tab on the first clamping-strap end, with a circumferential eccentric which presses onto the bent tab of this first clamping-strap end via a pressure plate. The clamping force is transmitted from the eccentric of the clamping lever to the two bent tabs of the two clamping-strap ends via the pressure plate. A disadvantage of this clamping device is that, in the event of a high clamping force and in view of the given unfavourable lever arm, a high bending moment acts on the bent tabs at the two clamping-strap ends and distorts these tabs. The necessary clamping force is therefore not obtained, with the result that the user has to make several readjustments. A further essential disadvantage is that a high surface pressure is effective on the sliding face between the eccentric of the clamping lever on the one hand and the pressure plate on the other hand. In theory, linear contact takes place in this region. Under high clamping forces, there is the danger that the surface of the sliding track will be destroyed due to an excessive surface pressure. The result is digging in and seizing. The clamping lever can then still be actuated only with the greatest effort.